The invention relates to a cell for the fused salt electrolytic reduction of aluminum oxide for the production of metallic aluminum, the said cell comprising an insulated tank or pot lined with carbon, an anode beam which runs longitudinally above the pot and can be lowered, anode rods which are mounted in rows on both sides of the anode beam, if desired devices mounted to the anode beam between the anode rods, a duct for collecting waste gases positioned along the middle between both rows of anode rods, and a covering comprising individual lids which are inclined downwards from the anode beam to the longitudinal edge of the pot and butt onto each other at their sides.
During the conventional production of aluminum by the fused salt electrolytic reduction of aluminum oxide, waste gases are produced. Before releasing these exhaust gases to the atmosphere, it is necessary to collect them and lead them to a scrubber unit.
It is known to meet this requirement by covering the reduction cell on all sides and conducting the gases off through a duct situated above the anode beam.
Some of the known systems comprise essentially a covering which is mounted horizontally below the anode beam, covering the anode rods (DE-OS 2 330 557) or the anode carbon blocks (DE-OS 2 251 898), and a further covering connected to the extremities of the horizontal covering and running at a slope down to the edge of the pot, the inclined covering being sub-divided into individual lids which can be raised singly or simultaneously by means of a frame to allow maintainance operations on the cell.
It is also known to employ a covering which is mounted on the anode beam itself (DE-OS 2 510 400), is inclined downwards from the anode beam to the longitudinal edge of the pot and can be tilted upwards about pivotal axes running in the longitudinal direction of the cell.
Patent DE-OS 2 263 348 describes a covering system comprising lid components which cover the whole of the electrolytic cell and can be slid inside each other. To carry out maintainance operations to the cell, a large part of the cell has to be uncovered by sliding back whole parts of the covering.
The covering systems representing the state of the art are relatively expensive and give rise to not insignificant difficulties. For example, when changing the anodes, either a large part of the cell must be uncovered and a large amount of waste gas released to the pot room, or else the change of anodes can not be carried out without considerable difficulty. To charge the cell with alumina or to pierce the crust, the covering must be raised along the whole length of the cell to allow proper maintainance work to be carried out, which again means releasing a considerable amount of waste gas. Furthermore, mounting the auxiliary beams normally used to raise the anode beams can not always be carried out without some difficulty.
A further disadvantage of the coverings representing the state of the art is that effective collection of the waste gases can be achieved only at relatively high cost. Furthermore, the retrofitting of existing non-hooded cells--if at all possible--can be carried out only at relatively high expense.
An object of the invention is therefore to develop a covering for a cell for fused salt electrolysis which allows existing, conventional electrolytic cells to be retrofitted, simply and made ecologically acceptable. It is a further object of the invention to make it possible to change anodes and to raise the anode beam with the existing facilities. Furthermore, it should be possible for one single man to manipulate the covering without need of additional facilities. The covering should also demonstrate a good cost/efficiency ratio.